Coupled Cavity TWTs are desirable because of their greater output power compared to helical TWT devices, and wide bandwidth compared to resonant gap devices such as klystrons. Additionally, compared to helical TWTs which can operate at a maximum frequency of 20 Ghz, coupled cavity TWTs can operate to 95 Ghz. Prior art single beam coupled cavity TWTs are limited in the maximum RF energy which may be present in the electron beam, which is governed by the beam current density, which in turn is limited by the lower operating voltage of the coupled cavity TWT.
A particular design issue of periodic permanent magnet (PPM) traveling wave tubes is illustrated in the prior art FIGS. 1A, 1B, and 1C. Prior art coupled cavity traveling wave tubes such as 150 of FIG. 1A use clamshell magnets 152 applied in pairs 152A and 152B straddling the TWT RF circuit, the magnets producing a magnetic field which is parallel to the device axis 154. FIG. 1B shows the cross section A-A of FIG. 1A, showing the axial front-facing dot and rear-facing x lines of magnetic flux from a PPM 152 clamshell assembly. The magnetic flux produced by such an assembly has a circularly symmetric but radially dependent non-uniform flux density as shown in the plot 160 of FIG. 1C showing the flux variation across the inner diameter of the clamshell magnet. The result of this non-uniformity is that the only uniform flux density location for placement of the electron beam is at the center axis 154 of the magnetic structure.
It is desired to provide a Traveling Wave Tube device for use as an amplifier or an oscillator, the traveling wave tube device having a plurality of electron beams that interact with an RF traveling wave such that energy is transferred between the electron beams and the RF traveling wave to cause axial bunching of the electron beams and increased energy in the RF wave. The input RF wave can be provided through an input RF port for an amplifier or from spurious excitation in an oscillator. The amplified RF wave is extracted through an RF output port.